1. Field of the Invention
The present invention relates to thin film comprising ruthenium, including a ruthenium thin film and a ruthenium oxide thin film (hereinafter inclusively referred to as a ruthenium thin film), formed by chemical vapor deposition (CVD), a ruthenium compound used as a ruthenium source in CVD, and a process for producing the thin film. More particularly, it relates to a ruthenium thin film formed by CVD using a specific organoruthenium complex, a .beta.-diketonatoruthenium useful as a ruthenium source in the CVD, and a process for producing the ruthenium thin film.
2. Description of the Related Art
Ruthenium thin film including a metallic ruthenium thin film and a ruthenium oxide thin film is expected to be applicable as a capacitor electrode of a thin film capacitor comprising a ferroelectric and high-dielectric substance used in memory devices, such as DRAM and FeRAM.
While thin film processing for forming a metallic thin film, a metal oxide thin film, and a complex metal oxide thin film includes sputtering, ion plating, pyrolytic coating, and the like, CVD is appreciated as the most suitable thin film deposition technique for manufacturing a ruthenium electrode for the above-described memory device capacitors from the standpoint of compositional controllability, coating performance on a surface with level differences, and matching with capacitor film production processing.
However, ruthenium compounds that have hitherto been proposed as a ruthenium source in CVD for ruthenium thin film deposition do not necessarily possess sufficient properties. That is, conventional ruthenium compounds for CVD are solid having high melting points and therefore need to be vaporized by sublimation or be maintained at higher temperatures above their melting points and have often given rise to problems in vapor supply and in-line transportation of raw material, such as shortage of vapor supply or variation in vapor supply with time. A solution CVD technique using a solution of a raw material compound in an organic solvent has been proposed in Japanese Patent Application Laid-Open Nos. 132776/93 and 186103/96. However, the solution is not stable enough for practical use because the ruthenium compound disclosed has small solubility in organic solvents, and the solution suffers from precipitation due to change in temperature, partial volatilization of the solvent, change in concentration, and the like.
Ruthenium compounds that have been proposed to date as a ruthenium source for CVD include tri(dipivaloylmethanato)ruthenium (melting point: 215.degree. C.; Japanese Patent Appln. Laid-Open No. 283438/94), and tri(diisobutyrylmethanato)ruthenium (melting point: 117.degree. C.) and tri(isobutyrylpivaloylmethanato)ruthenium (melting point: 134.degree. C.), both of which have a lower melting point than tri(dipivaloylmethanato)ruthenium (Tazaki, et al., Journal of the Chemical Society of Japan, No. 9, p. 648 (1997)), but none of them have furnished solutions to the above-described problems.